Synergistic interactions of endogenous opioids and cannabinoid systems

Cannabinoids and opioids are distinct drug classes historically used in combination to treat pain. Δ⁹-THC, an active constituent in marijuana, releases endogenous dynorphin A and leucine enkephalin in the production of analgesia. The endocannabinoid, anandamide (AEA), fails to release dynorphin A. The synthetic cannabinoid, CP55,940, releases dynorphin B. Neither AEA nor CP55,940 enhances morphine analgesia. The CB1 antagonist, SR141716A, differentially blocks Δ⁹-THC versus AEA. Tolerance to Δ⁹-THC, but not AEA, involves a decrease in the release of dynorphin A. Our preclinical studies indicate that Δ⁹-THC and morphine can be useful in low dose combination as an analgesic. Such is not observed with AEA or CP55,940. We hypothesize the existence of a new CB receptor differentially linked to endogenous opioid systems based upon data showing the stereoselectivity of endogenous opioid release. Such a receptor, due to the release of endogenous opioids, may have significant impact upon the clinical development of cannabinoid/opioid combinations for the treatment of a variety of types of pain in humans.     

Role of the Dynorphin/Kappa Opioid Receptor System in the Motivational Effects of Ethanol

Evidence has demonstrated that dynorphin (DYN) and the kappa opioid receptor (KOR) system contribute to various psychiatric disorders, including anxiety, depression, and addiction. More recently, this endogenous opioid system has received increased attention as a potential therapeutic target for treating alcohol use disorders. In this review, we provide an overview and synthesis of preclinical studies examining the influence of alcohol (ethanol [EtOH]) exposure on DYN/KOR expression and function, as well as studies examining the effects of DYN/KOR manipulation on EtOH's rewarding and aversive properties. We then describe work that has characterized effects of KOR activation and blockade on EtOH self‐administration and EtOH dependence/withdrawal‐related behaviors. Finally, we address how the DYN/KOR system may contribute to stress–EtOH interactions. Despite an apparent role for the DYN/KOR system in motivational effects of EtOH, support comes from relatively few studies. Nevertheless, review of this literature reveals several common themes: (i) rodent strains genetically predisposed to consume more EtOH generally appear to have reduced DYN/KOR tone in brain reward circuitry; (ii) acute and chronic EtOH exposure typically up‐regulate the DYN/KOR system; (iii) KOR antagonists reduce behavioral indices of negative affect associated with stress and chronic EtOH exposure/withdrawal; and (iv) KOR antagonists are effective in reducing EtOH consumption, but are often more efficacious under conditions that engender high levels of consumption, such as dependence or stress exposure. These results support the contention that the DYN/KOR system plays a significant role in contributing to dependence‐ and stress‐induced elevation in EtOH consumption. Overall, more comprehensive analyses (on both behavioral and mechanistic levels) are needed to provide additional insight into how the DYN/KOR system is engaged and adapts to influence the motivation effects of EtOH. This information will be critical for the development of new pharmacological agents targeting KORs as promising novel therapeutics for alcohol use disorders and comorbid affective disorders.     

创伤性脑损伤患者血浆β-内啡肽强啡肽A_(1-13)水平的研究

目的 探讨内源性阿片肽在创伤性脑损伤发病机制中的作用.方法 采用放射免疫分析法(RIA)测定30例全麻颅脑手术患者和30例全麻非颅脑手术患者术前、术后及30例正常人血浆β-内啡肽(β-endorphin,β-EP)和强啡肽A_(1-13)(dynorphin,DynA_(1-13))含量.结果 ①60例手术患者术后血浆β-EP含量显著升高(P<0.01),两组比较差异无统计学意义(P>0.05);②颅脑手术患者术后DynA_(1-13)含量显著升高(P<0.01),与非颅脑手术患者比较差异有统计学意义(P<0.01);③不同部位颅脑手术患者血浆β-EP和DynA_(1-13)含量比较差异无统计学意义(P>0.05).结论 内源性阿片肽在创伤性脑损伤病理生理过程中发挥的作用不同.β-EP在机体应激状态时普遍升高,血浆DynA_(1-13)含量是创伤性脑损伤的特异性指标,DynA_(1-13)含量与脑损伤部位无关.     

Conceptualizing withdrawal-induced escalation of alcohol self-administration as a learned,plasticity-dependent process

This article represents one of five contributions focusing on the topic “Plasticity and neuroadaptive responses within the extended amygdala in response to chronic or excessive alcohol exposure” that were developed by awardees participating in the Young Investigator Award Symposium at the “Alcoholism and Stress: A Framework for Future Treatment Strategies” conference in Volterra, Italy on May 3–6, 2011 that was organized/chaired by Drs. Antonio Noronha and Fulton Crews and sponsored by the National Institute on Alcohol Abuse and Alcoholism. This review discusses the dependence-induced neuroadaptations in affective systems that provide a basis for negative reinforcement learning and presents evidence demonstrating that escalated alcohol consumption during withdrawal is a learned, plasticity-dependent process. The review concludes by identifying changes within extended amygdala dynorphin/kappa-opioid receptor systems that could serve as the foundation for the occurrence of negative reinforcement processes. While some evidence contained herein may be specific to alcohol dependence-related learning and plasticity, much of the information will be of relevance to any addictive disorder involving negative reinforcement mechanisms. Collectively, the information presented within this review provides a framework to assess the negative reinforcing effects of alcohol in a manner that distinguishes neuroadaptations produced by chronic alcohol exposure from the actual plasticity that is associated with negative reinforcement learning in dependent organisms.     

Propionic acid metabolism,ASD, and vitamin B12: Is there a role for environmental nitrous oxide?

Foley et al. (2014) published their findings in this journal on the role of prenatal exposure to propionic acid (PPA) and behavioral outcomes in treated rat pups. The authors show that PPA treated pups displayed subtle differences in behavior including nest seeking, novel object recognition, and locomotor activity. Others have previously proposed that PPA infusion in rat could represent a valid animal model of ASD since many of the diagnostic criteria for the disorder spectrum manifest under such conditions. A pathogenic makeover of gut microbiome to facilitate the growth of microbes capable of producing PPA, like Clostridia species, has been proposed as an infectious contributing etiology to the PPA model of ASD, however the reason for this pathogenic microbial overgrowth is not clear. This discussion highlights a previously identified novel environmental factor (i.e., nitrous oxide, N₂O) in the etiopathogenesis of ASD and related neuropathology and posits that altered PPA metabolism in ASD may represent a key manifestation of this particular exposure. Trace environmental exposure to N₂O may induce release of endogenous opioid peptides that have been shown to confer a virulence advantage to certain microbes, like Pseudomonas aeruginosa. Pathogenic overproduction of PPA in ASD may be a compensatory mechanism to curb this enhanced virulence potential. Therefore, future research on the PPA model of ASD should consider its role as a consequence of environmental exposure to N₂O.     

Targeting dynorphin/kappa opioid receptor systems to treat alcohol abuse and dependence

This review represents the focus of a symposium that was presented at the “Alcoholism and Stress: A Framework for Future Treatment Strategies” conference in Volterra, Italy on May 3–6, 2011 and organized/chaired by Dr. Brendan M. Walker. The primary goal of the symposium was to evaluate and disseminate contemporary findings regarding the emerging role of kappa-opioid receptors (KORs) and their endogenous ligands dynorphins (DYNs) in the regulation of escalated alcohol consumption, negative affect and cognitive dysfunction associated with alcohol dependence, as well as DYN/KOR mediation of the effects of chronic stress on alcohol reward and seeking behaviors. Dr. Glenn Valdez described a role for KORs in the anxiogenic effects of alcohol withdrawal. Dr. Jay McLaughlin focused on the role of KORs in repeated stress-induced potentiation of alcohol reward and increased alcohol consumption. Dr. Brendan Walker presented data characterizing the effects of KOR antagonism within the extended amygdala on withdrawal-induced escalation of alcohol self-administration in dependent animals. Dr. Georgy Bakalkin concluded with data indicative of altered DYNs and KORs in the prefrontal cortex of alcohol dependent humans that could underlie diminished cognitive performance. Collectively, the data presented within this symposium identified the multifaceted contribution of KORs to the characteristics of acute and chronic alcohol-induced behavioral dysregulation and provided a foundation for the development of pharmacotherapeutic strategies to treat certain aspects of alcohol use disorders.     

给药途径对强啡肽A1—13抑制吗啡依赖大鼠戒断症状的影响

目的研究不同给药途径对强啡肽A1-13(Dyn)抑制吗啡依赖戒断症状的影响.方法采用剂量递增法建立大鼠吗啡身体依赖模型;吗啡依赖大鼠戒断症状采用sc 5mg*kg-1纳洛酮激发;Dyn对吗啡依赖大鼠戒断症状的影响采用侧脑室、脊髓及静脉内注射Dyn后,对大鼠经纳洛酮激发后60min内可数和不可数的戒断症状进行评分的方法进行.结果静脉内注射100μg*kg-1 Dyn可短暂抑制戒断症状;髓鞘内注射4μg*kg-1 Dyn可明显抑制绝大部分的戒断症状;侧脑室注射Dyn对吗啡依赖大鼠戒断症状无显著的抑制作用.结论 Dyn抑制阿片类物质戒断症状可能主要是通过脊髓水平起作用的.     

Dynorphin-independent spinal cannabinoid antinociception

Spinal antinociception produced by delta 9-tetrahydro-cannabinol (Δ⁹-THC) and other cannabinoid agonists has been suggested to be mediated by the release of dynorphin acting at the kappa opioid receptor. Alternatively, as cannabinoid receptors are distributed appropriately in the pain transmission pathway, cannabinoid agonists might act directly at the spinal level to inhibit nociception, without requiring dynorphin release. Here, these possibilities were explored using mice with a deletion of the gene encoding prodynorphin. Antinociceptive dose–response curves were constructed for spinal Δ⁹-THC and WIN 55,212-2 in prodynorphin knock-out mice and in wild-type littermates. WIN 55,212-2 and Δ⁹-THC were equipotent in the wild-type and prodynorphin knock-out mice. Spinal pretreatment with a kappa opioid receptor antagonist, nor-binaltorphimine (nor-BNI), did not alter the dose–response curves for either WIN 55,212-2 or Δ⁹-THC in prodynorphin knock-out and wild-type mice. However, the same dose of nor-BNI used blocked U50,488H-induced antinociception in both wild-type and prodynorphin knock-out mice, confirming kappa opioid receptor activity. Pretreatment with SR141716A, a cannabinoid receptor antagonist blocked the antinociceptive actions of both WIN 55,212-2 and Δ⁹-THC. These data support the conclusion that antinociception produced by spinal cannabinoids are likely to be mediated directly through activation of cannabinoid receptors without the requirement for dynorphin release or activation of kappa opioid receptors.     

Electroacupuncture attenuates bone cancer-induced hyperalgesia and inhibits spinal preprodynorphin expression in a rat model

Cancer pain impairs the quality of life of cancer patients, but opioid intervention can cause significant side effects that further decrease quality of life. Although electroacupuncture (EA) has been used to treat cancer pain, its mechanisms are largely unknown. To examine its effects and underlying mechanisms on cancer pain, we injected AT-3.1 prostate cancer cells into the tibia to induce bone cancer in the male Copenhagen rat. The resulting pain was treated with 10 Hz/2 mA/0.4 ms pulse EA for 30 min daily at the point equivalent to the human acupoint GB30 (Huantiao) between days 14 and 18 after the injection. For sham control, EA needles were inserted into GB30 without stimulation. Thermal hyperalgesia, a decrease in paw withdrawal latency (PWL) to a noxious thermal stimulus, and mechanical hyperalgesia, a decrease in paw withdrawal pressure threshold (PWPT), was measured at baseline and 20 min after the EA treatment. Preprodynorphin mRNA and dynorphin were determined by RT-PCR and immunohistochemistry, respectively. Thermal and mechanical hyperalgesia developed ipsilaterally between days 12 and 18 after cancer cell inoculation. EA significantly (P < 0.05) attenuated this hyperalgesia, as shown by increased PWL and PWPT, and inhibited up-regulation of preprodynorphin mRNA and dynorphin compared to sham control. Intrathecal injection of antiserum against dynorphin A (1–17) also significantly inhibited the cancer-induced hyperalgesia.These results suggest that EA alleviates bone cancer pain at least in part by suppressing dynorphin expression, and they support the clinical use of EA in the treatment of cancer pain.     

Content of Dynorphins and k-Opioid Receptors in Distinct Brain Regions of C57BL/6 and DBA/2 Mice

Differences in the activity of various components of the endogenous opioid system under basal conditions and after ethanol exposure have been reported between strains and lines of animals showing either high or low ethanol consumption. The objective of the present studies was to investigate the presence of differences in (a) the density of k-opioid binding sites, (b) the content of prodynorphin mRNA, and (c) the content of dynorphin peptides in distinct brain regions between the C57BL/6 (ethanol-preferring) and the DBA/2 (ethanol-avoiding) mice. Results indicated that the C57BL/6 mice have a higher content of k-opioid binding sites and dynorphin A1-13 in the amygdala, and dynorphin A 1–8 in the ventral tegmental area, whereas the DBA/2 mice presented a significantly higher content of k-opioid binding sites, prodynorphin mRNA, as well as dynorphin A 1–13 and dynorphin A 1–8 peptides in the nucleus accumbens and septum. In addition, the DBA/2 mice presented a higher content of k-opioid receptors in the periaqueductal gray and dynorphin A1-13 and dynorphin A 1–8 in the caudate putamen. Because enhanced stimulation of the k-opioid receptors at the level of the nucleus accumbens has been associated with decreased dopamine release and aversive states, the higher content of k-opioid receptors, prodynorphin mRNA, and dynorphin peptides (the endogenous ligand of k-binding sites) in regions of the limbic system of the DBA/2 mice may play an important role in determining their low alcohol consumption.